Chris
It makes a lot of sense. I checked mine, and it's 5-12-8 as you thought.
And the vacuum pipe is connected to the the throttle plate at the rear carb.
So, at idle we have very little vacuum, and we have very little force on
the weights in the distributor, so we shouldn't have any advance really.
Or should we, you say that the advance at idle is mechanic?
As engine speed rise we get more advance from the weights and and more
advance from the vacuum. But when does it stop?
Is the advance from the weights proportional to the engine speed or
something else? At what engine speed do the weights start to produce
advance, and at what speed do we have to most advance.
And when do we have the highest vacuum, at half throttle perhaps?
I'll tell you the reason I'm investigating this. Last summer I was asked
by a friend to take a look at his overdrive. It didn't work as it
should. It turned out to be an electrical problem, so that was easily
fixed. But while test driving his car I noticed that it didn't really
work above 3000 RPM, it just misfired and was generally miserable. I
began to suspect the ignition timing, and he told me that he some time
in the past had had some problem with the vacuum unit. So he replaced it
with a unit from what we think a Sprite. I don't know yet what profile a
Sprite has, and I haven't checked if I can see any numbers on his unit
yet. Since last summer I have replaced points, capacitor and spark plugs
on his car. Rotor and cap are in good condition. I have also changed his
carb linkage to a standard set up from what looked to be a complicated
home made construction that didn't really work, why someone had changed
it in the first place is beyond my understanding. So now the carbs can
at least be adjusted in the correct way.
I haven't yet tested the car on the road after these repairs, it's still
winter (sort of) here, but I'll make a try next week. It will be very
interesting. It runs fine on idle at least.
Today I also checked on a BJ8, and it's also 5-12-8, and the pipe is
connected at the throttle plate. That car has a leak in the vacuum pipe,
so I doubt it works as it should. But that will be a later problem.
Perhaps I should get myself a dyno!! Have never seen one.
Best regards, Per in Sweden
Chris Dimmock skrev 2012-04-19 01:28:
Hi Per,
That's correct. Sort of. Healeys generally get all their advance at idle
mechanically, not by vacuum. Is your vacuum connected to the Su or manifold??
Not sure specifically about a tri carb setup.
Perhaps I should have said the difference is "opposite" at idle.
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